It would be a good blog idea for someone to recommend the current sweet spot for bitcoin mining rigs. People would donate bitcoins to such a blog.

I'm actually just trying to figure out that sweetspot myself, there is a lot of overhead, so getting the GPU setup right is important: better GPU -> Faster payback of overhead but also more expensive upfront investment.

I'm starting to realise that there is no single sweetspot, that fits everybody's needs.